1. Field of the Invention
The present invention relates generally to a spark ignition timing control system for an internal combustion engine, such as an automotive internal combustion engine. More specifically, the invention relates to a spark ignition timing control for suppressing jerking during engine acceleration.
2. Description of the Background Art
In general, spark ignition timing is determined relative to MBT based on preselected ignition timing control parameters, such as engine load, engine speed and so forth. The spark ignition timing for each engine cylinder is set at a timing, at which a crank reference signal representative of 70.degree. or 66.degree. before TDC (hereafter "70.degree. BTDC") of each engine cylinder in compression stroke is output. Crankshaft angular position is monitored by counting crank position signals which are generated at predetermined angles, e.g. 2.degree. or 1.degree. increments of crankshaft angular displacement. Spark ignition is initiated at the crankshaft angular position matching the set spark ignition timing. Such general spark ignition timing control has been discussed in the Japanese Patent First (unexamined) Publication (Tokkai) Showa 59-126071.
On the other hand, there have been developed various electronic control systems for controlling engine and engine accessory control with substantially high precision. For example, it has become popular to control fuel delivery amount for engine cylinder in a manner precisely corresponding to the engine load. In modern fuel injection control systems, high precision and high response ability to fuel demand has been acheived. In such fuel injection control, acceleration enrichment is performed in response to acceleration demand which is represented by increase of throttle angular position. By acceleration enrichment, engine output torque increase precisely corresponds the acceleration demand.
However, because of intertia moment, vehicle speed and engine speed cannot be made to increase quickly enough to follow to increase of the engine output torque. This creates a torsional resonance of the engine block on the engine mounts which causes jerking of the vehicle body. Especially, in case of transversely mounted engines, wherein the magnitude of jerking tends to be amplified by the rotational torque created due to inertia of the engine block in a direction matching the direction of jerking. This clearly degrades drivability and riding comfort of the vehicle.